External grinder with an auxiliary grinding wheel

ABSTRACT

EXTERNAL GRINDER OF GENERALLY RECTILINEAR OVERALL SHAPE HAVING AN UPPER PLANE WHICH IS INCLINED TOWARD THE BACK AT AN ANGLE OF APPROXIMATELY 20* IN RELATION TO THE HORIZONTAL WITH PROVISION FOR THE OPERATOR WITHIN THE RECTILINEAR SHAPE AND WITH THE MAIN TABLE LOCATED AT THE FRONT OF THE OPERATOR AND A GRINDING SET AT THE SIDE OF THE OPERATOR, THE WHOLE MACHINE RESTING ON THREE LEGS AT LEAST ONE OF WHICH IS ADJUSTABLE AS TO HEIGHT, THE FRAME OF THE MACHINE BEING ESSENTIALLY COMPOSED OF TWO WATER-TIGHT VATS FORMING INTERLOCKING CAISSONS FILLED WITH A REFRIGERATION LIQUID ARRANGED FOR CONSTANT CIRCULATION. THE CONSTITUENT ELEMENTS OF THE MACHINE ARE TOOLED PERPENDICULARLY AMONG THEMSELVES AND ARE PROVIDED WITH AN OPENING AND THE ADDED PARTS ARE CIRCULAR, THE APPARATUS BEING PROVIDED WITH A MAIN GRINDING WHEEL WITH A MOVABLE CARRIAGE MOVING PERPENDICULARLY TO THE TRAJECTORY OF THE TABLE HOLDING THE PART TO BE GROUND ON A MAN CARRIAGE WHICH IS MOVABLE PERPENDICULARLY TO THE AFOREMENTIONED TRAJECTORY OF THE TABLE HOLDING THE PARTS, AND AN AUXILIARY GRINDING WHEEL HAVING A CARRIAGE WHICH MOVES OBLIQUELY WITH RESPECT TO THAT TO MAIN GRINDING WHEEL ON THE SAME MAIN CARRIAGE, THE MACHINE BEING PROVIDED WITH AN ELECTRONIC CONTROL SO THAT AS SOON AS ONE OR THE OTHER OF THE TWO WHEELS HAS SELECTIVELY REACHED THE POSITION CORRESPONDING TO THE FICTIOUS ZERO FROM WHICH A NUMERICAL COUNT MAY BEGIN,   THE FORWARD PROGRESS IS BROUGHT ABOUT BY THE MOVEMENT OF THE MAIN CARRIAGE BEARING THE GRINDING SET. THE MAIN CARRIAGE BEARING THE GRINDING SET IS ARRANGED TO SLIDE UP ON TWO LATERAL GUIDES WHILE ITS FORWARD PROGRESS IS OBTAINED BY MEANS OF JAC-SCREW PLACED BETWEEN THE TWO GUIDES AND NEARER TO THE MAIN GRINDING WHEEL. THE SCREW CAUSING FORWARD PROGRESS TO THE MAIN CARRIAGE IS OF THE MOTOR-REDUCER TYPE WITH ELECTRONICAL NUMERICAL COUNTING THE LEAD SCREW IS ASSOCIATED WITH A SLEEVE NUT ATTACHED TO THE MAIN CARRIAGE THROUGH COMPENSATING BELLOWS MEANS. THE TABLE HOLDING THE PART TO BE GROUND HAS A FIXED TAILBLOCK WHICH CONSTITUENTS THE ZERO READING.

NOV. 2, 1971 T 3,616,576 EXTERNAL GRINDER WITH AN AUXILIARY GRINDING WHEEL Filed Jan. 14, 1969 5 Sheets-Sheet 1 EXTERNAL GRINDER WITH AN AUXILIARY GRINDING WHEEL Filed Jan. 14, 1969 J. PIAT Noy. 2, 1971 5 Sheets-Sheet 2 Nov. 2, 1971 J. PIAT 3,616,516

EXTERNAL GRINDER WITH AN AUXILIARY GRINDING WHEEL Filed Jan. l4, 1969 s Sheets-Sheet 5 3,616,576 EXTERNAL GRINDER WITH AN AUXILIARY GRINDING, WHEEL Filed Jan. 14. 1969 J. PIAT Nov. 2, 1971 5 Sheets-Sheet &

NOV. 2, 1971 T 3,616,516

EXTERNAL GRINDER WITH AN AUXILIARY GRINDING WHEEL Filed Jan. 14, 1969 5 Sheets-Sheet 5 2 54 P Nqj 38 36 I W ,1

I: N I Z Lu.

United States Patent EXTERNAL GRINDER WITH AN AUXILIARY GRINDING WHEEL Jean Piat, La Varenne, France, assignor to Etablissements Piat, Montreuil, Seine-St. Denis, France Filed Jan. 14, 1969, Ser. No. 790,956

Claims priority, application France, Jan. 16, 1968,

136,274 Int. Cl. B24b 49/14 US. Cl. 51-165.73 13 Claims ABSTRACT OF THE DISCLOSURE External grinder of generally rectilinear overall shape having an upper plane which is inclined toward the back at an angle of approximately 20 in relation to the horizontal with provision for the operator within the rectilinear shape and with the main table located at the front of the operator and a grinding set at the side of the operator, the whole machine resting on three legs at least one of which is adjustable as to height, the frame of the machine being essentially composed of two water-tight vats forming interlocking caissons filled with a refrigeration liquid arranged for constant circulation. The constituent elements of the machine are tooled perpendicularly among themselves and are provided with an opening and the added parts are circular, the apparatus being provided with a main grinding wheel with a movable carriage moving perpendicularly to the trajectory of the table holding the part to be ground on a main carriage which is movable perpendicularly to the aforementioned trajectory of the table holding the parts, and an auxiliary grinding wheel having a carriage which moves obliquely with respect to that of the main grinding wheel on the same main carriage, the machine being provided with an electronic control so that as soon as one or the other of the two wheels has selectively reached the position corresponding to the fictitious zero from which a numerical count may begin, the forward progress is brought about by the movement of the main carriage bearing the grinding set. The main carriage bearing the grinding set is arranged to slide up on two lateral guides while its forward progress is obtained by means of a jack-screw placed between the two guides and nearer to the main grinding wheel. The screw causing forward progress of the main carriage is of the moto-reducer type with electronical numerical counting. The lead screw is associated with a sleeve nut attached to the main carriage through compensating bellows means. The table holding the part to be ground has a fixed tailblock which constitutes the zero reading.

This invention deals with a grinder of a completely original idea as compared to presently known grinding machines, which when compared with these gives it very important advantages which will become obvious in the course of the description of the invention.

The grinding machine according to the invention is characterized first of all by the fact that it is of generally rectilinear overall shape, the upper plane of which is inclined toward the back of an angle of approximately 20 degrees in relation to the horizontal, the operator being placed inside the right angle and having, in front of him, the main table and, at his side, the grinding set, which has the advantage of enabling him to have an excellent supervision of the work being done, away from any water projection and from eventual debris should the grinder accidentally shatter during the work.

The whole machine rests on three legs of which at least one is adjustable in height, so as to arrive at a perfect thermic isolation of the machine with relation to the 3,616,576 Patented Nov. 2., 1971 ground and thus avoid any baneful influence of temperature variations on the ground on the geometry of the machine.

The frame of the machine is essentially composed of two water-tight vats forming interlocking caissons, these caissons being filled with a refrigeration liquid in constant circulation so as to arrive at a perfect general stabilization of the temperature of the machine.

All the constituent elements of the machine are tooled always perpendicularly among themselves and always have an opening while the added parts are always circular, which has a double advantage, on the one hand, it allows for a particularly simple and fast assembling of both the constituent and added elements, on the other hand, it renders a greasing in closed circuit possible without having to set up and kind of hydraulic transmission.

The grinding is done by means of two grinding wheels: one main grinding wheel with a moveable carriage, it moves perpendicularly to the trajectory of the table holding the part to be ground, on a main carriage which can itself move perpendicularly to the afore-mentioned trajectory of the table holding the parts, and an auxiliary grinding wheel whose carriage moves obliquely with respect to that of the main grinding wheel on the same main carriage, the electronic control of the machine, of any known type, being adjusted in such a way that as soon as one or the other of the two wheels has selectively reached the position corresponding to the fictitious zero from which the numerical count begins, the forward progress is brought about by the movement of the main carriage bearing the grinding set.

Following a favourable method of application of the invention, the main carriage bearing the grinding set is slid up on two lateral guides while its forward progress is obtained by means of a jack-screw placed between the two guides and nearer to the main grinding wheel so as to have a perfect dynamic equilibrium of the said carriage.

The screw which causes the forward progress of the main carriage should be of the moto-reducer type with electronic numerical counting bringing a lead screw in rotation with a very high degree of precision, which screw leads to a sleeve nut attached to the main carriage through compensating bellows means which prevents all dangerous polar modifications during the movement of the carriage along its guides.

The table holding the part to be ground has a tail-block fixed in place which constitutes the zero reading of the machine and a feeding head-stock carriage which can move length-wise on the aforementioned table, this table also moves length-wise on the frame of the machine, along the guide rail activated by a screw.

The guide rail is made up of a plate attached to /1 of its back part on the frame of the machine while its front part has at least one groove in which a heating electric resistance is placed so as to be able to obtain a bending of the said rail at will and to provide for the flexion compensation of a part being ground or the accomplishment of a curved grinding.

The main parts-holding table rests on the guide rail by means of two adjustable screws placed near its extremities, which enables one to incline it in relation to the said rail and, consequently, do conic grinding.

The jack-screws used to obtain the inclination of the parts-holding table should be resistant potentiometer types giving a high degree of precision.

The resistance of each potentiometer is made up by two wires wound to non-touching spires on a cylinder having, for this purpose, two helical grooves while the runner is made up of a spiral spring closed upon itself so as to make up a circular tore rolling around the resistance inside a ring-shaped element attached to the extremity of the moveable element of the jack-screw.

To obtain the best possible electric contact between the spring forming the runner and the electric resistance spires, these spires should be truncated, this also makes it possible to have the resistance of the potentiometer vary in function of the position reading of the runner on the electric resistance, so as to have a non-linear curve of resistance which takes into consideration the inclination which the parts-holding table might assume in relation with the guide rail.

Other characteristics, advantages and particularities of this invention will become obvious in the course of the description given next referring to the enclosed drawings which represent, in a purely explicative and not at all restrictive manner, one possible way of carrying out this invention.

On these drawings:

FIG. 1 is a view in perspective of a grinding machine of the type of the invention;

FIG. 2 is a draft on a larger scale;

FIG. 3 is a transversal cut of it, made following the line III-III of FIG. 2;

FIG. 4 is a view of detail representing a transversal cut, made following line IVIV of FIG. 2, of the feeding system of the main carriage with the grinding wheels;

FIG. 5 is a view in detail on a larger scale representing the mounting of the lead-screw of the carriage holding the grinding set;

FIG. 6 is a view in detail on a larger scale representing a transveral cut of the rail-guide of the main table;

FIG. 7 is a schematic view on a length-wise axial cut of one of the control jack-screws of the main table;

FIG. 8 is a view in detail on a larger scale representing very schematically the runner of the resistant potentiometer of the jack-screw of FIG. 7; and

FIG. 9 is the electric plan of a possible mounting of the control jack-screws of the main table through a conventional canalization 300 and nozzle 300 In general the grinding machine shown as an example on the drawings assumes the overall shape of a square designated by the general reference 1 where the superior plane is inclined by an angle of approximately 20 degrees in relation to the horizontal.

The operator is placed inside the right angle which is completely free of any obstacle which might annoy him.

On branch 1,, of the square which is in front of him, a single table 2 can slide length-wise and on it are mounted: on the one hand, the tail-block 3 which cannot move and whose position cannot be changed and which constitutes the zero reading of the machine, as we shall see in greater detail later on; and on the other hand the feeding headstock 4 which can moreover move along table 2 activated by a feeding motor 5 which we will discuss again later.

Table 2 can be pulled length-wise along a guide-rail 6 which is of a particular type and which will be described in detail later on, activated by the lead-screw 7 which in turn is taken into rotation by a special kind of motor 8 which we shall also discuss again later.

'On branch 1 of the square, a main carriage 9 having two auxiliary wheel-carrying carriages, can slide.

Carriage 9,, holds the main grinding wheel 10,, and moves following a trajectory which is perpendicular to that of table 2 while carriage 9 holds a finishing grinding wheel 10 and moves following an oblique trajectory in relation to that of carriage 9 The working of the under part of the wheel-holder will be described in detail later on.

Before going any deeper into the description, we can see even now that, because of its very particular general plan, which has just been described generally, the machine built according to the invention presents important advantages when compared with the classic grinding machines, some of these are the following:

Other than the fact that the operator has complete freedom of movement in his operations near the machine, he is also not subjected to any water projection since the main grinding wheel 10 A is parallel to him. This position of the grinding wheel also has the advantage of eliminating the risk of projection of debris upon the operator in the case of an accidental shattering of the grinding wheel.

Because of the inclination of the whole with respect to the horizontal and of the position of the grinding wheel, the operator has an excellent view of the part being ground and which is even more important sees no shadows of it. The result is a particularly comfortable supervision of the work of the machine.

Moreover, the operator is in an excellent position to introduce perforated cards for automatic control of the machine programmer which is placed in a box which can be easily attached to the rear part of branch 1,; of the machine which includes the wheel-holding carriage.

The inclination of the machine, apart from providing the lowering of the center of gravity of the whole, has the advantage of facilitating the control, of the main table 2 as well as of the main carriage 9 and the auxiliary wheelholding carriages 9 and 9 In fact, table 2 rests of its own weight on the inclined slide 6 while the grinding set also moves back by the force of its own weight.

Following another general characteristic of this invention, the whole machine rests on three legs such as 11 11 of which one is adjustable in height.

This arrangement, besides making it possible to ensure an easy adjustment of the balance of the machine, accomplishes, in a particularly simple manner, a thermic isolation of the machine in relation with the ground. The immediate and particularly interesting result of this is preventing the variations of the temperature of the ground, which are much slower than those of the machine, from having a dangerous influence on the geometry of the machine following strains. This is the case with the classical machines which rest directly on the ground.

According to another characteristic of this invention, the frame of the machine (see FIG. 3 more particularly) is essentially composed of two water-tight vats forming caissons 12, 13 which interlock, for example by means of screws such as 14.

In the superior part of the front vat 12, are found; the oil tank 15; a length-wise groove with a square section 16 in which are placed the lead-screw 7 and its feeding motor 8, a grease pump and the table carriage; and a length-wise cavity 17 in which the electric cabling is located.

Two parallel columns 18 18 are attached to the superior part of the lateral caisson 13, these serve as guides to the main carriage 9 of the grinding set, this will be discussed in detail later on.

The two compartments 12 and 13 are filled with a refrigeration liquid in constant circulation in order to obtain a general stabilization of the temperature of the machine. A pump (not shown) placed appropriately draws the liquid in the lateral compartment 13 to throw it back into the front compartment 12 while a second pump (not shown) ensures the spraying of the part tooled and of the grinding wheels, following its cooling action, the liquid moves into compartment 13. It should be noted that the converter group is advantageously placed in the cooling liquid.

Apart from its action as temperature stabilizer, the arrangement of the two constituent compartments 12 and 13 makes it possible to replace caisson 13 and its grinding set with another caisson having a different grinding set, such as for example a group of three or four grinding wheels placed perpendicularly or not to the displacement axis of table 2.

According to another general characteristic of the machine, all constituent elements of the machine are always tooled perpendicularly the ones to the others and always have an opening while the added elements are always circular.

If we add to this the fact that all the electric motors used are of the type having a water-tight gear case and an oil bath, we notice that the above mentioned characteristic of the machine makes it possible: on the one hand, to have a particularly simple and fast mounting of both the added and constituent elements, this can take a few minutes for the former and up to a few hours at the most for the latter; on the other hand, of having a greasing system is closed circuit without having to install any kind of transmission, the hydraulic circuit being de facto existent by the simple mounting of the constituent elements one on the other. The oil pump is best installed on the feeding shaft of the lead-screw 7 ensuring the forward progress of the main electric table 2.

According to an essential characteristic of this invention, the grinding, as we have seen earlier, is ensured by means: (a) of the main grinding wheel which moves perpendicularly to the guide rail 6 of the main table 2; (b) of the finishing grinding wheel 10;; which moves obliquely with respect to this guide rail 6.

According to the invention, the control of the two truing wheels is assured as follows:

Each grinding wheel, as for example wheel 10,; which can distinctly be seen on FIG. 3, is mounted on an auxiliary carriage 19,, which can run in a slide 20 which is fixed to the main carriage 9, activated by a motor which acts on a rack following a well-known method.

It is important to note that, according to an essential characteristic of the invention, the electronic programmer planned for the back of the machine and which can be of any known type and thus is not an integral part of the invention should be able to give orders such as:

(1) The feeding motor of each auxiliary wheel holding carriage, 19 for example, stops the latter as soon as the corresponding grinding wheel, 10 in this case, comes in contact with a cutter wheel 3 at that moment table 2 is of course in its extreme left position on FIG. 2. This cutter should be fixed on the shaft of an alternator which' orders the immediate stopping of the corresponding carriage for example by cutting the feeding current. This operation makes it possible to determine the fictitious zero from which the numerical count of the main carriage is undertaken;

. (2) The parts-holding table is brought to its work position with an eventual return of the main carriage if the diameter of the part to be tooled makes it necessary;

(3) That the feeding of the motor be guaranteed, so that it can bring about the forward movement of the main carriage 9 by a numerical count starting from the fictitious zero which was determined earlier until the final reading of the part is reached;

(4) That the return of the main carriage be assured to the next work or operation.

. The working cycle for an operation such as just been described for grinding wheel 10,, is the same insofar as grinding wheel 10;; is concerned.

According to the best method of carrying out this invention, the movement of the main carriage 9 along the guides 18 and 18 is assured by means of a jack-screw, designated by the general reference 21 on FIG. 2, which is found placed between guides 18 and 18 as close as possible to the main grinding wheel 10 so as to obtain the best equilibrium possible of the grinding set and as rectilinear a movement as possible of this latter.

This jack-screw 21 should be made up of a moto-reducer with electronic numerical count placed inside a water-tight gear case.

According to the best method of carrying out this invention as shown on FIGS, 4 and 5, the water-tight gear case in which the mote-reducer 21 is installed, is integral with carriage 9 while the lead-screw 23 is fixed on shaft 22 of the moto-reducer and drives a sleeve nut integral with a cylinder 25, which is itself fixed on the back face 12 of the front vat 12.

According to a characteristic of the construction of the invention, the nut 24 is mounted on a brace 26 attached to the base of cylinder 25, through bellows means 27, bearing against the one hand, against a circular thrust-block 26 of the brace, and on the other hand, on a shoulder 28 of the sleeve nut 24.

This bellows means has the advantage of making possible a particularly easy assembling of the controls of the forward movement of the carriage and of the compensation of the carriage in cartesian coordinates without any polar modification, which would have a particularly dangerous influence on the exactness of the grinding done by the grinding wheels.

It should be noted that the motor 8 which leads the lead-screw 7 for the forward movement of the main table 2 as well as that of the oil pump eventually, is also of the moto-reducer type with an electronic numerical count as was discussed earlier for the main carriage 9 bearing the grinding set.

We saw earlier that, according to a characteristic of the planning of the machine according to the invention, table 2 is unique. It has, at one of its extremities, the tail-block 3 which is fixed into place and serves as point Zero for the machine. At its other extremity, a carriage 29 is installed and holds the feeding headstock 4 and its motor 30 which is like all the others with a water-tight gear case and an oil bath. Carriage 2 9 has the general shape of a square, the front branch is parallel to the axis joining the two points, his branch is massive and senves as a counter weight for the equilibrium of the whole which moves activated by 'a motor 5 placed vertically whose motor shaft has a pinion driving a length-wise rack of table 2. It possesses a device which assures its instantaneous clamping and unclarnping in position of operation.

We saw earlier that table 2 slides along a guide rail 6. This rail, according to one of the characteristics of the invention, is made up of a plate (see FIGS. 3 and 6 more particularly) which is fixed only on A of its length, on shoulder 12 of the front compartment 12 of the frame by means of two thrust-blocks such as 31.

Moreover, the front part of the plate-rail 6 has at least one length wise groove on its lower part in which an electric resistance 32 is placed.

iIt is immediately obvious that this electric resistance makes it possible, when it is fed, to heat the front extremity of plate 6 and to bring about a bending of the rail by deformation of the plate whose back part is fixed only at its two extremities and kept at room temperature.

Tests which the applicant has made have shown that we could thus obtain 'a bending of 20 to 25 microns of the guide rail, a bending which makes it possible to either compensate for grinding errors or the fiexion of a part being ground in an easy and efiicient manner, or even to do a bent grinding voluntarily.

It is evident that the electric resistance 32 will be controlled by a thermistance of any appropriated type in order to render the system perfectly reliable and automatic.

According to another characteristic of the invention, table 2 rests on the guide rail 6, by means of two adjustable jack-screws 33 33 which are approximately one meter away one from the others (see FIG. 2).

The control of the two jack-screws is accomplished, either by using electronic numerical count mo to-reducers which were discused earlier, or by using resistance potentiometers which We will discuss again later on.

V It appears that, because of this possibility of inclining table 2 with respect to the length-wise axis according to which this table moves, it is possible to do conic toolings.

If we adopt the solution of resistance potentiometers to assure the control of the jack-screws, we than then suitably use the method of carrying out the invention which is shown very schematically on FIGS. 7, 8, and 9.

According to this solution, the fixed part 34 of each jack-screw is made integral in any suitable way with table 2 while the moveable element 35 of this jack-screw is made integral with the part forming a projection with the guide rail 6.

The real resistance of the potentiometer 36 is constituted by two wires wound on non-touching spires on a cylinder 37 which has to this end two helical grooves 37 37 (see FIG. 8) in Which the resistance wires are wound. Cylinder 37 is attached by one of its extremities to the bottom of cylinder 34 in the axis of this cylinder and inside a coaxial recessed hollow 38 made in the moveable element 35 and having a sufficient length to make it possible for the latter to reach the bottom of cylinder 34. The feeding of the wires is made through the bottom of cylinder 34'.

According to a characteristic of the invention, the runner of the potentiometer designated by the general reference 39 on FIG. 7 is composed, as it is shown on FIG. 8, of a spiral spring 39 which is closed upon itself so as to make up a tore having a circular section which can roll on the spires of the resistance 36, when the element 35 moves in the direction of the arrows F or F The spring 39,, is placed in a ring-shaped cavity 40 open on its internal face and mounted on the free extremity of the moveable element 35 as shown distinctly on FIG. 8.

To obtain the best electrical contact possible between the spring 39 and the spires of the resistances 36, these spires are truncated following a cylinder whose traces H H H H' are shown by a broken line on FIG. 8.

Besides guaranteeing an excellent contact, this makes it possible, if desired, to have the resistance vary in function of the reading simply by incurving the cylinder of traces H -H H -H in the desired direction. This makes it possible to have a non-linear curve of resistance taking into consideration the inclination which the partsholding table might take with respect to the guide rail 6.

It seems important to note that because of the inclination of the spires of the two constituent wires of resistance 36 with respect to those of spring 39,, the contacts between the above mentioned elements are perfectly punctural and thus of a high degree of precision. This makes it possible to determine with an equally high degree of precision the value of the two resistances thus delimited on the total resistance 36.

From the point of view of a schematic understanding of the electric mounting, each of the jack-screws 33 33 such as the one which we have just described can be fed in a Wheatstones bridge as sketched as an example on FIG. 9. On this figure, R and R represent fixed resistances of which R is adjustable, for example, and serves for the posting of the order. The toric runner 39 determines, along the double solenoid 36, two elements of respective resistances a and b.

We immediately see that if we feed the bridge in a continuous current between points B and C for a given value of R with respect to R the movable element 35 will move until the runner 39,, reaches the required position to restart the values of the resistances a and b so that these will balance the resistances R and R respectively. At that moment the current annuls itself in the measure branch A-39 schematized by the milliamperemeter 41, and the system stops.

We notice that in this way we can obtain the desired inclination of table 2 with respect to the length-wise displacement axis.

According to a suitable variable of carrying out this invention, the resistance a, as a value, can be constituted by the potentiometer of the right-hand jack-screw and the resistance b by the potentiometer of the left-hand jack-screw.

We see that, in this way, we automatically obtain the desired inclination of table 2 corresponding to the posting of the value R when the values of a and b correspond,

8 by the displacement of the runners, to the respective values of the resistances R and R We saw earlier that because of the plan of the toric runner 39a rolling on the spires of the resistance 36, we could obtain a precision of the type of the second of the arc, both in the definition of the point of contact and of the values of the resistances a and b; it follows that the stopping positions of the movable elements 35 of the jac screws 33,, and 33 and, consequently, the angle of inclination of table 2 with respect to its trajectory, can be determined with the same degree of precision.

It will be obvious to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown in the drawings and described in the specification.

What is claimed is:

1. An external grinder with main table, Water projection means and grinding wheel, essentially characterized by being L-shaped and with said main table having an upper plane inclined rearwardly at an angle of approximately 20 degrees with respect to the horizontal, a location for the operator being inside a right angle whereby, in front of the operator, is the main table and, at the operators side is located a grinding set, and whereby the operator has excellent supervision of work being done, away from any water projection and from eventual debris should the grinding wheel accidentally shatter during the grinding.

2. The external grinder of claim 1 rests on three legs, of which at least one is adjustable in height, whereby there is obtained a perfect thermic isolation of the external grinder in relation with the ground and thus avoid any dangerous influence of the variations of the ground temperature on the geometry of the machine.

3. The external grinder of claim 1 having a frame which is essentially made up of two water tight vats forming caissons which are integral with one another, these cais sons being filled with a refrigeration liquid in constant circulation whereby there is obtained an optimum general stabilization of the temperature of the external grinder.

4. The external grinder of claim 1 having all its constituent elements tooled perpendicularly among themselves and having an opening while its added elements are circular, whereby simple and fast mounting is possible of both the constituent and the added elements, and greasing may be accomplished in closed circuit without having to install any type of hydraulic transmission.

5. The external grinder of claim 1 wherein the grind ing work is done by means of two grinding wheels; a main grinding wheel with a movable carriage which moves perpendicularly to the trajectory of the main table holding the part to be ground, a main carriage moves perpendicularly to the said trajectory of the parts-holding table; a second grinding wheel whose carriage moves obliquely with respect to that of the main grinding wheel on the same main carriage.

6. The external grinder apparatus of claim 1 and a jackscrew guaranteeing the forward movement of the main carriage of the motoreducer type with an electronic numerical count driving a lead-screw in precision rotation, said screw driving a sleeve nut whichis integral with the main carriage through compensating bellows means so as to prevent dangerous polar modification in the course of the movement of the carriage along its guides.

7. The external grinder of claim 1 wherein the table holding the part to be tooled has a tail-block whose position cannot be changed and constitutes the zero reading of the external grinder, and a feeding head-stock carriage which can move lengthwise on the table, said table being movable lengthwise on a frame of the external grinder, along a guide rail, activated by a screw.

8. The external grinder of claim 1 including guide rail composed of a plate attached on approximately threefourths of its back part on a frame of the external grinder while its front part has at least one groove in which is placed a heating electric resistance so as to obtain a bending of the rail at will whereby to allow for the flexion compensation of a part being ground and the potential of doing a curved grinding.

-9. The external grinder of claim 1 wherein a main parts-holding table rests on a guide rail by means of two adjustable jack-screws placed near its extremities, whereby it is possible to incline said table with respect to the rail and do conic grinding.

10. The external grinder of claim 9, wherein the jackscrews for obtaining the inclination of the main parts holding table are of the resistance potentiometer type giving a high degree of precision.

11. The external grinder of claim 10 wherein the resistance of each potentiometer is constituted by two wires wound to two non-touching spires on a cylinder which has, for this purpose, t-wo helical grooves while a runner is made up of a spiral spring which is closed upon itself so as to constitute a circular tore rolling around the resistance inside a ring-shaped element attached to the extremity of the movable element of the jack-screw.

12. The external grinder of claim 11 wherein to obtain optimum electric contact between the spring making up a runner and the spires of the electric resistance, said spires are truncated, whereby it is possible to vary the resistance of the potentiometer in function of the position reading of the runner on the electric resistance so as to have a non-linear curve of resistance taking into consideration the inclination which the main parts-holding table might take with respect to the guide rail.

13. The external grinder of claim 1 wherein a main carriage holds the grinding set and is slideable up on two lateral guides with forward movement being facilitated by means of a jack-screw located between the two guides and closer to the grinding wheel whereby to obtain an optimum dynamic equilibrium of said carriage.

References Cited UNITED STATES PATENTS 1,575,968 3/1926 Bryant 5195 2,127,210 8/1938 Dunbar 5'195 2,171,892 9/1939 Richardson 51-95 2,950,578 8/1960 Fouquet 51-95 2,985,988 5/1961 Johnson et a1 51166 X LESTER M. SWINGLE, Primary Examiner U.S. C1. X.R. 5195 WH, 166 PB 

